A system for optical wireless communication (OWC) is a wireless communication system using optical wavelengths. The OWC may be classified into image sensor communications enabling optical wireless communications using an image sensor as a receiver, high-rate photodiode (PD) communications using a high-speed, bidirectional network to enable mobile wireless communications using light and a high-speed photodiode receiver, and low-rate PD communications which refer to a wireless light identification (ID) system using an LED as a low speed photodiode receiver. High-rate PD communications may include:                indoor office/home applications, like in conference rooms, general offices, shopping centers, airports, railways, hospitals, museums, aircraft cabins, libraries, etc.,        applications in data center/industrial establishments and secure wireless applications, like manufacturing cells, factories, hangars, etc.,        applications in vehicular communications, like vehicle-to-vehicle communications and vehicle-to-infrastructure communications, and        applications in a wireless backhaul network, like in a small cell backhaul network, a surveillance backhaul network or applications for local area network (LAN) bridging.        
An optical wireless communication system operating in the above referenced high-rate PD communications mode allows for a networked mobile communication using multiple distributed semiconductor light sources, like light emitting diodes (LEDs) or lasers, for example, for the first three applications mentioned above, as well as a single-link high-speed communication for the last mentioned application. The high-rate PD communications involve the following:                packet-based transmission of data,        an efficient use of the available optical bandwidth of a given luminaire,        data rates scalable from 1 Mbps to 10 Gbps,        latencies between 1 ms and 30 ms,        a dimming support,        allow for asymmetric communications,        provide for the handling of the handover and interference coordination,        the ability to coexist with ambient light and other lighting systems,        support MIMO and other cooperative signaling process with negligible impact on latency,        provide an efficient and reliable feedback and control channel for adaptive transmissions, multiple user support, MIMO support, cooperative signal processing, variable current modulation schemes, and        defined metrics for reporting to high layers in the communication protocol using an open interface.        
The above referenced considerations for a high-rate PD communication mode are described, for example, in reference [1]. Further, a coordinated multipoint transmission using a signaling on the X2 interface is described, for example, in reference [2].
According to an embodiment, a system for providing an optical wireless communication with a mobile device may have: a plurality of optical frontends coupled to a central point, each of the plurality of optical frontends configured to provide for an optical wireless communication with the mobile device; and a network controller coupled to the central point, wherein the network controller includes a data flow control device configured to control the data flow between each of the optical frontends and the central point, the data flow control device being configured to operate responsive to a control signal from the network controller, the control signal indicating which of the plurality of optical frontends serves the mobile device, wherein an interface from the plurality of optical frontends to the network controller is configured to exchange control signals between the network controller and the plurality of optical frontends, wherein a plurality of mobile devices communicate with the optical frontends using coordinated links, wherein the mobile devices and the optical frontends estimate the physical interference channel before a coordinated transmission and respective metrics reports are conveyed by the optical frontends to the network controller as an input for the interference coordination and handover, and wherein, depending on the link situation, the network controller is configured to initiate a handover event by rerouting traffic paths between the network controller and the plurality of optical frontends and to control the transmission of the mobile devices and the optical frontends to minimize an interference.
In accordance with the inventive approach, embodiments concern an optical wireless communication. An optical wireless link in an optical wireless communication system only has a real-valued non-negative channel. However, assuming that a sufficiently high constant bias current is applied, the optical wireless channel may be modeled as a real-valued multipath channel with additive white Gaussian noise so that algorithms may be applied that may similar to those used for mobile radio transmissions.
In accordance with embodiments of the present invention, multiple optical wireless links are provided which have an overlapping coverage area within a cell of the communication system to provide for a coordinated transmission. This may cause an inter-cell interference so that cooperative transmission algorithms may be applied.
Further, in an optical wireless communication system mobility management of mobile users may be needed so as to allow for a correct handover and for interference coordination. In accordance with the inventive approach, this achieved by adopting the cloud radio access network (C-RAN) architecture known from mobile radio applications also to optical wireless communications. The C-RAN architecture provides a central control (CC) functionality for handling the handover management and the interference management. In accordance with the inventive approach, adopting the C-RAN architecture for optical wireless communications allows placing the central control functionality in a “natural” network node. For example, when considering an optical wireless communication system as it might be used in an industrial production hall or in a home, there will be central points where all signals of the light sources (=the wireless access points for the optical wireless communication system) come together. In an industrial environment, such central points may be certain aggregation nodes like switches and routers in a common IT infrastructure, and within a home, the central point may be a common fuse box. The central point may host the central control functionality for handover and interference management, which is somehow similar to a local cloud. The CC may also provide for data processing capabilities by exploiting its location and the close proximity to the switches/routers in an IT infrastructure allowing for a faster data processing when compared to a processing originating from the frontend. Further, at the CC multiple signals from multiple frontends may be jointly processed.
In accordance with the inventive approach, the optical frontends provide the interface to the CC, for example via existing network paths in the PHY and MAC layers. As mentioned above, the CC is located at “natural” network nodes, i.e. is located nearby the actual wireless frontends (other than central control elements in a radio based system which are typically situated hundreds of kilometers away from the user), so that a very fast information exchange is possible allowing for a fast interference coordination if users are mobile and the channel to serving interfering cells changes quickly. A low-latency handover from one access point to another access point is also enabled.
In accordance with embodiments, when transmitting a packet over the wireless link, the corresponding routing information is stamped at the Ethernet transport layer at as a VLAN (virtual local area network) address into each individual packet. The links from the CC to the frontends are assumed to be pre-configured for each access point, like an aggregation node inside a local IT network, so that, by changing the stamp used at the CC, the packet will go another way. For example, when considering an Ethernet transport layer with a largest packet size to be 1500 byte and a lowest data rate to be 1 Mbps, 12 ms are needed to transport the largest packet over the wireless link. When considering a data rate of 12 Mbps, the largest packet may be transferred in 1 ms so that, when signaling to a user for which the access point changes (handover needed), the route for the next packet may be changed after that 1 ms, and even less at higher speed. In a similar way, when implementing a corresponding functionality also in the wireless terminal, the route of uplink packets may be rapidly changed.
By introducing a centralized controller (CC) located at a local node, all decisions and low-layer routing operations, for example needed for instantaneous interference management and handover, may be made locally, thereby achieving a low latency for mobile data links without external control from a core network. Further, all transport may be Ethernet-based so that existing low-cost technology may be used. The security and queue functionality implemented in the centralized controller applies stamps to each individual packet according to control information received from the controller and, may also be inside the mobile terminal, so that fast routing of packets between the controller and the mobile terminal in a downlink connection and in uplink connection is possible even when the access points for the mobile user in the wireless communication system change.